Settings menu item in stock2 doesn't work

The underlying problem is that we lacked a RenderObjectWrapper for the
RenderView, which meant we couldn't handle changing the RenderObject that was
the root of the RenderView. This CL introduces a RenderViewWrapper and uses it
in a new AppContainer widget root. This change allows us to make App a
non-magical Component that is inserted into the AppContainer in the newly
introduced runApp function.

R=ianh@google.com

Review URL: https://codereview.chromium.org/1184823006.

examples/game/main.dart

@@ -23,7 +23,7 @@ void main() {
 
 void allLoaded(ImageMap loader) {
   _loader = loader;
-  new GameDemoApp();
+  runApp(new GameDemoApp());
 }
 
 class GameDemoApp extends App {

examples/stocks2/lib/stock_app.dart

@@ -12,8 +12,6 @@ import 'stock_settings.dart';
 
 class StocksApp extends App {
 
-  StocksApp({ RenderView renderViewOverride }) : super(renderViewOverride: renderViewOverride);
-
   NavigationState _navState = new NavigationState([
     new Route(name: '/', builder: (navigator) => new StockHome(navigator)),
     new Route(name: '/settings', builder: (navigator) => new StockSettings(navigator)),
@@ -37,7 +35,7 @@ class StocksApp extends App {
 
 void main() {
   print("starting stocks app!");
-  App app = new StocksApp();
+  runApp(new StocksApp());
   WidgetAppView.appView.onFrame = () {
     // uncomment this for debugging:
     // WidgetAppView.appView.debugDumpRenderTree();

examples/widgets/container.dart

@@ -51,5 +51,5 @@ class ContainerApp extends App {
 }
 
 void main() {
-  new ContainerApp();
+  runApp(new ContainerApp());
 }

examples/widgets/hello_widgets.dart

@@ -11,5 +11,5 @@ class HelloWorldApp extends App {
 }
 
 void main() {
-  new HelloWorldApp();
+  runApp(new HelloWorldApp());
 }

examples/widgets/navigation.dart

@@ -73,5 +73,5 @@ class NavigationExampleApp extends App {
 }
 
 void main() {
-  App app = new NavigationExampleApp();
+  runApp(new NavigationExampleApp());
 }

examples/widgets/sector.dart

@@ -137,7 +137,7 @@ class SectorApp extends App {
 }
 
 void main() {
-  App app = new SectorApp();
+  runApp(new SectorApp());
   WidgetAppView.appView.onFrame = () {
     // uncomment this for debugging:
     // WidgetAppView.appView.debugDumpRenderTree();